Design Tokens: Provide color alternatives for automatic dark mode (swr.de-NEU)

[sjockers]

swr.de-NEU comes with automatic dark mode (based on OS settings). This means that we need to add dark mode alternatives for all colors currently provided as design tokens.

• Add color alternatives for dark mode, e.g. using light-dark or prefers-color-scheme
• Add a storybook page for dark mode testing
• Test the color alternatives with existing projects within swr.de

Ideally, color switching should happen within the components library and not require additional code in the repos that use the design tokens.

[awesomephant]

💀💀💀

[awesomephant]

• Colours: Maybe replicate some of the SWR semantic colours into our own system, ie --sds-color-border-primary-default